Here's my one piece of advise. Get EVERYTHING in writing before you throw them the keys. And I mean everything!!
From where the passives go, to how they are going to mount the midbasses. Where they are going to use the dynamat, what they are mounting the amp to, where, etc, etc, etc....
Seriously, account for everything, assume absolutely nothing.
Install is one of those areas where you get what you pay for IMO.